fun main() {
    val builder = StringBuilder()

    // 区間スケジューリングの使い方分からない……
    val (n, m) = readInputLine().split(" ").map { it.toInt() }

    val timeList = mutableListOf<Pair<Int, Int>>()

    repeat(m) {
        val (d, hm, o, hmo) = readInputLine().split(" ")
        val (h, m) = hm.split(":")
        val (ho, mo) = hmo.split(":")
        timeList.add(Pair(d.toInt() * 24 * 60 + h.toInt() * 60 + m.toInt(),
                          o.toInt() * 24 * 60 + ho.toInt() * 60 + mo.toInt() + 1))
    }

    timeList.sortBy { it.first }
    timeList.sortBy { it.second }

    var ans = 0

    val room = IntArray(n) { -1 }

    for (t in timeList) {
        var maxIndex = -1
        for ((i, r) in room.withIndex()) {
            if (r <= t.first && (maxIndex == -1 || room[maxIndex] < r)) {
                maxIndex = i
            }
        }
        if (maxIndex != -1) {
            room[maxIndex] = t.second
            ans++
        }
    }

    builder.appendln(ans)

    print(builder.toString())
}

fun readInputLine(): String {
    return readLine()!!
}